Move the Main instruction from register to virtual

also needs a branch in register.
This way the register level is self sufficient
(noticed while writing debugger)

lib/virtual/instructions/virtual_main.rb

@@ -0,0 +1,19 @@
+module Virtual
+
+  # This starts the Virtual machine machine at the given function.
+
+  # The implementation is most likely a jump/branch , but since we have the extra layer
+  # we make good use of it, ie give things descriptive names (what they do, not how)
+
+  class VirtualMain < Instruction
+    include Positioned
+
+    def initialize method
+      @method = method
+    end
+    attr_reader :method
+    def word_length
+      4
+    end
+  end
+end